Dual cylinder-concrete pump

ABSTRACT

THERE IS DISCLOSED A DUAL CYLINDER-CONCRETE PUMP IN WHICH EACH OF THE TWO CONVEYING CYLINDERS IS OPERATIVELY ASSOCIATED WITH A POSITIVELY CONTROLLED THREE-WAY VALVE OPERATIVELY ASSOCIATED WITH EACH CONVEYING CYLINDER FOR THE SELECTIVE CONNECTION OF EACH SUCH CONVEYING CYLINDER WITH A FILLING FUNNEL AND A CONVEYING CONDUIT OR LINE. ACCORDING TO THE INVENTION A THIRD THREE-WAY VALVE IS ARRANGED BETWEEN THE DISCHARGE OPENINGS OF BOTH THREEWAY VALVES ASSOCIATED WITH THE CONVEYING CYLINDERS AND THE AFORESAID CONVEYING CONDUIT.

`lune 6, 1972 K, SCHLECHT 3,667,869

DUAL CYLINDER-CONCRETE PUMP Filed Feb. 26, 1971 2 SheeS-Sheei l Q a as 55 @why Fig. 2 Figa /N z/EN To f? HT/"ORNEL/ June 6, 1972 K. SCHLECHT 3,667,869

DUAL CYLINDR-CONCRETE PUMP filed Feb. 26, 1971 2 Sheets-Sheet 2 K f f k T V 76 77 78 80 |13 12 Fig. l.

/NVENTOR fmm. scHLfaHT RUDRNEY United States Patent Oi'ce 3,667,869 Patented June 6, 1972 3,667,869 DUAL CYLINDER-CONCRETE PUMP Karl Schlecht, 91 Echterdingerstrasse, D-7024 Bernhausen-Stuttgart, Germany Filed Feb. 26, 1971, Ser. No. 119,182 Claims priority, application Germany, Mar. 4, 1970, P 20 10 112.6 Int. Cl. F04b 17/00, 35/00, 23/04, 41/06, 15/02 U.S. Cl. 417-346 8 Claims ABSTRACT OF THE DISCLOSURE There is disclosed a dual cylinder-concrete pump in which each of the two conveying cylinders is operatively associated with a positively controlled three-way valve operatively associated with each conveying cylinder for the selective connection of each such conveying cylinder with a lling funnel and a conveying conduit or line. According to the invention a third three-way valve is arranged between the discharge openings of both threeway valves associated with the conveying cylinders and the aforesaid conveying conduit.

BACKGROUND OF THE INVENTION The present invention relates to a new and improved dual cylinder-concrete pump, that is to say a pump unit for conveying concrete which is of the type possessing two conveying cylinders working in phase opposition, and wherein a three-way valve is associated with each of both conveying cylinders for the selective connection of each conveying cylinder with a filling funnel and a conveying conduit or line.

In pumps of this type the alternation of the pressure stroke of both conveying pistons as well as the switchover of the conveying pistons from the pressure stroke to the suction stroke, and vice-versa, in other words the change-over of the conveying pistons from the rear deadcenter position and the front dead-center position, occurs practically simultaneously with the switching of the valves associated with both conveying cylinders. This simultaneous switching of all valves and the simultaneous reversal or switch-over of the conveying pumps is brought about in that the associated drive cylinder is simultaneously impinged with pressurized oil from an oil reservoir or storage.

Furthermore, individual pumps are already known to the art which are equipped with hydraulic remote or follow-up controls in which, when the conveying piston has reached the front dead-center position the associated lthree-way valve is switched, thereafter the rearward movement of the conveying piston is initiated and at the other conveying cylinder the valve is switched, and thereafter the movement reversal of the conveying piston is initiated.

However, insofar as their course of movement and their mode of operation are concerned these pumps differ only very slightly from the first-mentioned pumps with simultaneous switching of the valves and reversal of the conveying pistons.

In the case of pumps of the last-mentioned type the switching operation results in a brief interruption of the conveying operation brought about by both conveying pistons. What is common to both pump types is the fact that the pressure stroke of the one conveying piston only then begins after completion of the pressure stroke of the other conveying piston.

Apart from the time which is required for the switching or reversal of the valves and the interruption of the conveying action brought about thereby, it is here also so be mentioned that because of the additional prolongation of the conveying pause during switching or reversal from one conveying cylinder to the other conveying cylinder, the concrete, generally because of a more or less large content of air, must be initially compacted to the conveying pressure prevailing in the line before it can be pressed out of the conveying cylinder and into the conveying line. In the case of stiff plastic concrete having a degree of compaction or compression of about 1.5, that is, possessing a consistency which is usable during working of the concrete, this means that a conveying piston with a stroke of about 1.5 meters only then begins with the actual conveying operation after it has already moved through 0.5 meter of the theoretical conveying path. This means that the volumetric eiciency of such concrete pumps drops to about 0.65 owing to the content of air and voids of the concrete.

This unfavorable volumetric eiciency is furthermore still additionally impaired in that during high conveying pressure and during the momentary reversal or switching of both three-way valves there exists for a brief time a short-circuit between the conveying conduit or line and the iilling funnel. Consequently, a not inconsiderable quantity of concrete escapes during the switching operation in the direction of the filling funnel and is pushed back into such.

Additionally, the volumetric efficiency is also reduced since a negative pressure exists during the suction operation which is caused by the friction of the concrete at the walls of the valves and the conveying cylinders. If the concrete already from the start possesses a certain air content and therefore possesses a predetermined degree of compaction which is governed thereby, then, due to the suction action the portion of the volume which remains free of concrete within the conveying cylinder is still further enlarged.

This phenomena, especially when working with very light concrete which contains a great deal of air, can result in a complete breakdown of the conveying operation.

Althought it is possible to balance out the reduced volumetric eiciency by increasing theV drive efiiciency, still the remaining conveying requirements during reversal or change of the stroke and the thus brought about pump surges constitute a considerable drawback in practice. By increasing the piston displacement and correspondingly reducing the number of strokes it is possible to achieve a certain improvement, yet it is not possible to thus attain a complete prevention of these pump surges.

SUMMARY OF THE INVENTION Accordingly, there is still present a read need in the art for concrete pump units of the aforementioned type which are not associated with the drawbacks explained above prevailing in the prior art constructions. Therefore, a primary object of the present invention is to provide concrete pumps of the aforementioned type which effectively and reliably fulfill the existing need in the art and overcome the previously discussed disadvantages associated with the prior art constructions.

Another and more specific object of the present invention relates to the provision of a dual cylinder-concrete pump which affords also for concrete containing air, a uniform, practically surge-free conveying of the concrete without interruption.

The last-mentioned objective of the invention is particularly achieved in that a third valve, preferably likewise positively controlled, is arranged between the discharge openings of both three-way valves associated with both conveying cylinders and the conveying conduit.

A particularly uniform, continuous concrete conveying action can be achieved by means of a follow-up control actuated by terminal switches for controlling both conveyingl pistons in both conveying cylinders and' the actuation of the three-Way valves connected after such conveying pistons. The terminal switches serve to actuate not only the conveying pistons but also the third three-way valve, In the event each conveying piston is equipped with a hydraulic drive then the hydraulic lines leading to both drive cylinders can contain two respective serially connected three-way control valves.

According to a particularly advantageous-embodiment the third three-way valve is also provided with a hydraulic drive which'is formed by a piston displaceable in a pressure cylinder and an electro-valve controlling piston movement. Moreover, in order to actuate this electro-valve terminal switches are provided at the hydraulic drives of the conveying cylinders, which also serve to simultaneously switch the drive elements controlling the three-way valves arranged at the conveying cylinders.

The follow-up control for the movement of the conveying pistons and the actuation of the valves advantageously occurs 'in Vaccordance with a follow-up control program inA such a manner that during the change-over the one conveying piston movesl through a pressure stroke, whereas the other conveying piston carries out a suction stroke at a higher velocity and, triggered by the terminal switch arranged at the associated'drive cylinder-the aforementioned other conveying piston when reaching its rear dead-'center position is switched-over so as to perform a forward movement. Moreover, at the same time, triggered by the terminal switch, the valve arranged at the associated conveying cylinder is closed towards a lling funnel by means of its associated working cylinder and associated valve. The other conveying piston during a pressure stroke pre-compacts the sucked-up concrete within the cylinder to essentially the same pressure which is exerted upon the concrete during the same time by the one conveying piston which is still carrying out its pressure stroke, and when this one piston approaches its front dead-center position, owing to a thereby triggered pulse of the associated terminal switch via a four-way valve and the associated drive cylinder, communicates the additional valve at the conveying cylinder with the common conveying line or conduit. Thereafter, due to a terminal switch the other conveying piston is switched over from the compaction stroke to the conveying stroke in that a three-way valve connects the hydraulic line of the drive cylinder associated with the other conveying piston with a conveying or feed pump, and at the same time, likewise due tothe action of a pulse of a terminal switch of the drive cylinder, the suction stroke for the one conveying cylinder and its associated conveying piston is initiated in that the hydraulic line for the drive cylinder connects the other conveying piston by means of magnetic valves with a return flow and a tank, and the valve arranged after the one conveying cylinder opens in the direction of the tilling tunnel, which opening action is triggered by the same control pulse of the terminal switch, whereupon this work cycle alternatingly repeats.

Advantageously the pistons of both conveying cylinders are continuously subjected to the action of a return or restoring force bringing about the suction stroke, this return or restoring force being exerted by a spring effective through the agency of a traction element, such as for instance a cable or the like.

By virtue of such follow-up control it ispossible to control the movements of both conveying pistons `in both pump cylinders independently ot--one another.

BRIEF DESCRIPTION oF THE DRAwrNGs The invention will be better understood and objects other than those set forth above, wiil become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:

FIG. l is a schematic representation of the essential components and control elements of a twin `piston-concrete pump or" the invention;

FIG. 2 is a diagram illustrating the switching program of a stepping switching mechanism serving as the followup control;

FIG. 3 is a modified switching program from that shown in PIG. 2; and l FIG. 4 is a longitudinal sectional view through a moditied form of conveying cylinder from that shown in the embodiment of FIG. 1.

DEAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawings, in the embodiment of equipment depicted in FIG. 1 and 2 the conveying cylinders have been designated `by'reference numerals land 2. The conveyed material is sucked-out of the common tillingor suction funnel or container 9 into both conveying cylinders 1 and 2 by the'conveying piston members 3 and 4 independently of one another. These conveying piston members 3 and 4 are equipped with the drive or work pistons and 26 respectively. Piston members 3 and 4,

" when carrying out their respective pressure stroke, disamounts of the conveyed material reaches the conduits lled with the hydraulic oil, and thus the cylinders 1 and 2 as well as the rear faces of the pistons 3 and 4 are flushed or washed free from any hardened cement or concrete residues.

The switching or reversal of the conveying pistons 3 and 4 is undertaken at their terminal positions through the agency of hollow constructed piston rods 21 and 22, within which there are arranged feeler rods 19 and 20. At the respective front ends of such feeler rods 19 and 2t) there are provided the contact or impact members,27 and 28 respectively. Cam members 29 and 30 mounted at the feeler rods 19 and 20 serve to actuate controlor terminal switches 61 to l64 when conveying pistons 3 and 4 assume their terminal positions.

The control pulses emanating from these control switches can be transmitted in pneumatic, hydraulicl or also electrical fashion to main control valves or other control devices, by means of which the individual control elements, such astor instance hydraulically actuated drive cylinders, can be controlled.

In the embodiment illustrated in the drawings there has been chosen for the sake of simplicity in illustration and explanation an electrical control with a conventional stepping or switching mechanism which, switched by control pulse, acts upon control valves constructed as magnetic valves possessing two respective control positions. The magnetic valves 51 to 57 are represented in the gures with conventional symbols as used in the control art. When these magnetic valves are subjected to current flow they assume one switching position, Without current iiow the other switching position under the action of the schematically illustrated springs providing a return or restoringl force. l 1

The drive system is supplied by a control oil pump 36 and a drive oil pump 37. The control pump 36 conveys oil via a storage charging valve 35 into an oil reservoir or storage means 34. As soon as a certain maximum pressure prevails in this oil reservoir 34 the liow of oil from the pump 36 is switched by valve 35 so that it circulates without pressure. The oil reservoir 34 can be, however, also supplied via a throttle-check valve from the circulation system of the drive pump 37 and pressure conduit 41.

A pressure equalization or balancing valve 38 ensures that oil always flows in the oil conduit 42 from the reservoir 34 with the same pressure as it is generated in the conduit 41 by the drive pump 37 as a function of the conveying pressure of the concrete pump.

Both of the conveying cylinders 1 and 2 open via connection conduits 11 and 12, defining discharge openings, into a common conveying line or conduit 16. The inventive proposed third valve 13 is provided at the location of intersection or meeting of these connection conduits 11 and 12. It is advantageous if this valve 13 is constructed in the same manner as the conventional three-way valve and 6 which are associated with both of the conveying cylinders 1 and 2 respectively. In order to preserve clarity in illustration there has been schematically shown in the drawing a simple ap valve 13 rotatable about axis or shaft 14. Flap valve 13 is actuated by a hydraulic cylinder controlled by magnetic valve 57. Both of the other three-way valves 5 and 6 are actuated by the respective hydraulic cylinders 7 and 8 controlled by respective magnetic valves 56 and 55.

Now it will be observed that a control cam 40 is mounted at the piston rod of drive cylinder 15. This control cam 40 acts upon both terminal switches 65 and 66 in the terminal positions of the three-Way Valve 13. Cam 40 and the terminal switches 65 and 66 could be, of course, mounted at a different location of the three-way valve 13. It is only necessary to ensure that a control pulse is triggered at the terminal positions of the threeway valve mechanism 13.

The control pulses transmitted to the stepping mechanism by the terminal switches 61 to 66 bring about in known manner actuation of the magnetic valves 51 to 57 in accordance with the switching program illustrated in FIG. 2. The letters a to f designate the individual switching positions. The graph illustrates which of the magnetic valves 51-57 controlling the hydraulic cylinders 7, 8, 15, 17 and 18 are energized in the individual switching positions and which terminal switch always delivers the switching pulse for switching to the next successive switching position. In FIG. 1 of the drawing there has been illustrated the momentary condition a where the conveying piston 3 carries out its pressure stroke and the conveying pistion 4 is in a position shortly prior to cornpletion of its suction stroke. By virute of the described coupling of a control switch with the magnetic valves, occurring through the agency of the stepping mechanism, and the action of the described hydraulic oil drive. `the following course of operation occurs:

The conveying piston 3 at a relatively low velocity carries out the pressure stroke which has been adjustedv -by the pump control or also appropriate valves. During this time the piston 4 carries out the suction stroke at a greater velocity, whereby pressurized oil flows from the reservoir 34 via the conduit or line 31 into the drive cylinder.

As soon as the piston 4 has reached the rear dead-center position terminal switch 62 releases a pulse, and thereby places the stepping mechanism into position b. The magnetic valve 5S is thus energized and reverses the hydraulic cylinder 8, so that the three-way valve 6 communicates the compartment of the conveying cylinder 2 with the connection conduit 12 of the conveying line 16. At the same time the forward movement or compaction phase of the conveying piston 4 begins with a relatively high velocity-or speed because pressurized fluid medium ows to the cylinder 18 from reservoir 34 via the pressure equalization valve 38, the conduit 42, the valve 54 which is energized in position b of the stepping mechanism and the non-energized valve 53. The piston member 4 then comes to rest when the same oil pressure has built-up in the pressure line 33 from the reservoir 34 as in the oil conduit 41 from which the piston 3 located in its conveying stroke receives its work energy through the agency of the drive cylinder 17 and the conduit 32.

Now after a certain period of time the conveying piston 3 arrives at its forward terminal position, whereupon switch 63 releases a pulse which further positions or indexes the stepping mechanism at position c, and as a consequence thereof actuates the drive cylinder 15 through the agency of the magnetic valve 57 and the three-way valve 13 is switched in such a way that the outlet or discharge opening of the three-way valve 6 associated with the cylinder 2 is connected with the conveying conduit or line 16. During this time the conveying piston 3 can still slightly move forwards, so that no pressure drop occurs in the conveying conduit 16.

As soon as the third three-way valve 13 has assumed its other position the terminal switch 66 is actuated, and thus, the stepping mechanism is switched over into position d. The magnetic valve 53 is energized, so that it communicates the pressure line 41 supplied by the work pump 37 with the conduit 33, in order that the hydraulic cylinder 18 receives the entire work power and can advance the conveying piston 4. At the same time the magnetic valve 51fis without current so that the conveying piston 3 can be retracted. The magnetic valve 56 is like` wise without current and via the hydraulic cylinder 7 causes switching of the three-way valve 5 so that the suction operation can begin in the conveying cylinder 1.

If the conveying piston 3 reaches its terminal position within the cylinder 1 with a great velocity or speed, then, the control switch 64 delivers a pulse, whereup on stepping mechanism is placed into position e. In this position e the conveying piston 4 continues to carry out its pressure stroke. However the magnetic valve 56 is energized, which switches the three-way valve 5 via the hydraulic cylinder 7, so that the interior of the conveying cylinder 1 is no longer open in the direction of the filling funnel 9, rather again opens in the direction of the connection conduit 11. At the same time the magnetic valve 52 is also energized, so that the conveying piston 3 can be advanced and thus there is achieved a pre-compaction of the concrete up to the actual conveying pressure as such is simultaneously exerted by the conveying piston 4. As soon as the conveying piston 4 has then reached its forward terminal position the terminal switch 61 delivers a pulse, whereupon the stepping mechanism is indexed into position f, in which the magnetic valve 57 is again energized, so that the third three-way valve 13 is pivoted back into the starting position depicted in the drawing by means of the hydraulic cylinder 15. At the end of this pivotal movement the terminal switch 65 switches the switching or indexing mechanism into position a, whereby the magnetic valves 52, 53 and 55 are without current, but, however, the magnetic valve 51 energized, so that all components can again assume the position of FIG. 1 and the cycle can again begin. During such time as the one piston conveys concrete the other piston always performs a starting vand compression movement, which is rendered possible by the third three-way valve 13. This mode of operation results in the fact that during the described operation at no period of time does there occur a pressure drop in the conveying line or conduit 16, so that the pump operates completely without surges and continuously with the same conveying speed.

With a view towards simplifying the control it is also possible to dispense with the use of both switches 65 and 66 and to carry out switching of the third three-way valve 13 analogous and simultaneous with the switching of the first two three-way valves 5 and 6. In such case there is then provided for the stepping mechanism a switching program as such has been illustrated in FIG. 3. This differs from the switching program of FIG. 3. This differs from the switching program of FIG. 2 in that there are missing positions c and f. Of course, with this arrangement, during the rapid reversal or switching operation a short-circuit can appear between the conveying line 16 and the suction funnel 9 which could lead to a brief pressure drop.

However, this drawback is to be weighed against the use in practice of a much simpler control operation utilizing less control switches and therefore also affording less source of disturbance or trouble. In any case, there is however maintained the principle of pre-compaction of the concrete in each conveying cylinder prior to the beginning of the actual conveying stroke of a piston and therefore prior to the beginning of the displacement or freed of the concrete into the conveying conduit 16.

The stepping mechanism previously considered can also be replaced by a dierent and known hydraulic, electrical or pneumatic remote or follow-up control. It is also conceivable to mix or commingle the mentioned three control possibilities with one another.

Just as it was possible to use for the inventive arrangement a hydraulic oil drive it is also possible to use a hydraulic water pump system as such has been depicted in FIG. 4. In this figure there has only been shown in side view one of both conveying cylinders of the twin concrete pump assembly. Here the conveying piston 113 is driven in conventional manner by means of the pressurized Water medium and is again retracted by means of a traction member or element 81 after the piston has reached its forward dead-center position. The return or restoring force exerted by the traction or pulling element 81 acts continuously, that is to say, also during the suctionand pressure strokes, in that this traction element, preferably constituted by a cable, is payed-olf a suitable roller 72. Within this roller or roll 72, rotatable about the axis or shaft 71, there is located a spiral spring or band spring 73. This spring is connected at one end 75 with the fixed shaft and at its other end 74 with the periphery of the cable Wheel and during the pressure stroke of the conveying piston 3 is stressed beyond its pre-bias.

`In the same manner the cable roll 72 can also be rigidly connected with the shaft 71, whereby this shaft 71 is extended out of the housing 70 and externally thereof is continuously acted upon by a torque or rotational moment, so that there is thus brought about return of the piston member 3.

The scanning of the terminal position of the conveying piston 3 can be achieved at the rear dead-center position by means of, for instance, the connecting or thrust rod 78. This rod 78 can be hingedly connected with a lever 76 and operatively connected by means of a shaft T7 with a terminal switch which, upon reaching the deadcenter position, delivers a signal for initiating the next switching operaton and for further indexing the stepping mechanism.

The forward dead-center position can be determined by another traction element which in the forward deadcenter position moves the rod 78 and therefore the shaft 77, whereby an appropriate control pulse is applied to the stepping mechanism and such is further indexed.

The water serving in this case as the pressurized fluid medium can be delivered by means of conduit 132 to a suitable location of the cable wheel housing 70. This connection line 132 corresponds to the oil line or conduit designated in FIG. l by reference character 32. The valves connected in front correspond in their function exactly to the valves AS1 to 54 of FIG. l. Of course, structurally they are designed in respect of the pressurized water medium, as is also the case for the pumps and the preceding arranged valves which in operation are the same or similar.

It is also conceivable to further simplify the drive and control and to accommodate such to the momentary construction and manner of use of the equipment. The illustrated embodiments, especially the selection of the valves 51 to 54, however provides the advantage that similar type elements can lead to a less expensive mass-produced construction.

It is also conceivable and possibly at times advantageous, for the purpose of controlling the speed of the suction stroke of the conveying pistons, to install an adjustable throttle valve 47 in the common return flow line or conduit `43: for the drive medium. In the case of a hydraulic oil drive there can be similarly used for the same purpose an adjustable throttle check valve 46 which is installed at the conduit 3,1 connected with the drive cylinders |17 and 18. In order to accommodate the speed of the suction stroke to the adjustable speed of the pressure stroke of the conveying pistons the valves 46 and 47 could be controlled as a function of the quantity of driving medium flowing in the conduit 41. In the most simple embodiment this automatic feedback coupling could be dispensed with in that the suction stroke of the pistons could proceed so rapidly by fixedly setting the valves 46 or 47, that the conveying piston has completed the suction stroke and the compaction stroke before the other conveying piston has reached its forward deadcenter position, even if such conveys with the largest pressure stroke-velocity determined by the drive pump 37.

While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims. Accordingly,

What is claimed is:

1. A dual cylinder-concrete pump comprising a pair of conveying cylinders, conveying conduit means and filling funnel means operatively connected with both said conveying cylinders, a respective positively controlled three- Way valve operatively associated with each conveying cylinder to alternately connect each said conveying cylinder with said filling funnel means and said conveying conduit means, both said three-way valves, defining a first and second three-way valve and having means providing discharge openings, and a third three-way valve arranged between said discharge openings of said first and second three-Way valves associated with said pair of conveying cylinders and said conveying conduit means.

2. The concrete pump as defined in claim 1, further including means for positively controlling said third threeway valve.

3. The concrete pump as defined in claim 2, further including a respective conveying piston in each of said conveying cylinders, follow-up control means possessing terminal switch means serving for controlling said conveying pistons in both said conveying cylinders and said first and second three-Way valves arranged after said conveying cylinders, said terminal switch means being actuated by said conveying pistons and said third three-way valve.

4. The concrete pump as defined in claim 2, further including a respective conveying piston in each of said conveying cylinders, hydraulic drive means provided for each conveying piston, said hydraulic drive means incorporating a respective drive cylinder means for each conveying piston and hydraulic lines which contain two respective series connected three-Way control valves.

5. The concrete pump as defined in claim 4, wherein said positively controlling means for said third three-Way valve includes hydraulic drive means comprising a piston displacea'ble in a pressure cylinder and electrovalve means for controlling piston movement, and terminal switch means for actuating said electrovalve means provided at said hydraulic drive means for said conveying cylinders, said terminal switch means also serving for the simultane ous switching of drive elements controlling said first and lecond three-way valves arranged at said conveying cyliners.

6. The concrete pump as defined in claim 1, wherein each conveying cylinder is provided with a piston, and means providing a restoring force for each said piston to continuously subject each piston to such restoring force bringing about a suction stroke for said pistons.

7. A concrete pump as defined in claim 6, wherein said means providing said restoring force comprises spring means effective via a traction element upon the associated piston of each conveying cylinder.

8. The concrete pump as dened in claim 4, further including a follow-up control operating in accordance with a follow-up control program which occurs in such a manner that during change-over one said conveying piston moves through its pressure stroke, whereas the other conveying piston at a higher speed performs its suction stroke, terminal switch means arranged at said drive cylinder means for triggering said other conveying piston when located at its rear dead-center position to switch over to forward movement, said terminal switch means simultaneously triggering said three-way valve arranged at the associated conveying cylinder of said other conveying piston so that said just-mentioned three-way valve is closed towards said lling funnel means through the action of an associated work cylinder and associated valve, said other conveying piston during its pressure stroke precompacting the sucked-up concrete in its associated cylinder at essentially the same pressure which is exerted upon the concrete during this time by said one conveying piston which is still located in its pressure stroke, and, when said one conveying piston has approached its forward dead-center position, clue to a thereby triggered pulse of its associated terminal switch means connects via a fourway valve and an associated drive cylinder means of said third three-Way valve said conveying cylinder of said other conveying piston with said conveying conduit means,

10 additional terminal switch means for switching said other conveying piston from its compaction stroke to its conveying stroke in that a three-way control valve connects a hydraulical line of the drive cylinder means associated with said other conveying piston with a conveying pump, said additional terminal switch means of said drive cylinder means of said third three-way valve simultaneously initiating a suction for said one conveying piston in that a hydraulic line of said hydraulic drive means for said drive cylinder means of said other conveying piston is connected by magnetic valve means with a return ow and a supply tank, said three-way valve arranged after said one conveying cylinder being triggered by the same control pulse of said additional terminal switch means and opening in the direction of said filling funnel means whereupon this working operation repeats in alternating fashion.

References Cited UNITED STATES PATENTS 3,266,435 '8/1966 Smith 417-900 X 3,477,380 11/ 1969 Johanson et al 417-900 ROBERT M. WALKER, Primary Examiner U.S. Cl. X.R. 

